As disclosed in U.S. Pat. No. 5,908,573, floor warming systems are known that incorporate electrically resistive heating elements. The heating element may be threaded through a meshwork mat which is in turn embedded in a floor beneath tiles, carpeting, or other finished flooring materials. The heating elements can be energized using household AC power, and they then apply heat to the floor in order to warm it as well as the overlying space.
Products of this type have been subject to a number of problems, most notably in the area of safety. One problem that can create a safety hazard occurs when workers installing either the floor warming system or the flooring materials inadvertently drive metal fasteners such as nails or staples into the heating elements or their lead wiring. The fastener can then be in contact both with a heating element conductor and another metal object such as a metal reinforcing rod or wire, a shower pan, or metal pipes extending in the floor. If the system is thereafter energized in this condition, a person may be standing on the shower pan or be in contact with a plumbing fixture or other metal object that is supplied with current through the short circuit provided by the fastener. This creates the potential for electrocution even if a ground fault circuit interrupter (GFCI) or other electrical protection device is installed.
Remodeling of floors in which floor warming systems have already been installed can also create safety hazards. Existing heating elements for floor warming systems have been provided with ground shields that are formed in a construction referred to as a "serve" construction. A serve type shield includes a series of wires wrapped in parallel around the heating wires in order to physically protect them and to provide an electrical ground for them. A serve wire construction provides less than satisfactory physical protection against sharp objects such as nails, staples, or pointed trowels of the type commonly used when laying tile. Consequently, the serve shield can be penetrated by the sharp metal objects, and this can expose remodeling workers to a potentially lethal electrical shock if the heating element is energized.
The serve shield may have enough wire to carry sufficient current to trip a GFCI protective device. However, if such protection is not installed or is installed improperly or is not functioning for some reason, a serve type shield has insufficient wire capacity to carry the current to ground in order to interrupt the electrical circuit. For this reason, the potential for lethal shocks is present when remodeling activity takes place and particularly in the absence of effective GFCI protection.
For the floor to be adequately warmed, the heating elements must be concentrated in a relatively dense pattern. As a result, the heating elements generate a significant electromagnetic fields (EMF) when current flows through them. Electromagnetic fields have been associated with medical problems including cancer, memory loss, and interference with the absorption of prescription drugs. Electrical appliances have been specially designed and redesigned in recent years to provide protection against undue human exposure to electromagnetic fields. However, many electric floor warming systems have at best minimal shielding against EMF exposure, so persons who are in proximity to the floor warming system can be subjected to possibly harmful electromagnetic fields.